To ameliorate the need to spend significant programmer time modifying parallel programs to achieve high-performance, while maintaining compact, comprehensible source codes, this paper advocates the use of telescoping languages technology to automatically apply, during the normal compilation process, high-level performance enhancing transformations to applications using a high-level domain-specific I/O library. We believe that this approach will be more acceptable to application developers than new language extensions, but will be just as amenable to optimization by advanced compilers, effectively making it a domain-specific language extension for I/O.The paper describes a domain-specific I/O library for irregular block-structured applications based on the KeLP library, describes high-level transformations of the library primitives for improving performance, and describes how a high-level domain-specific optimizer for applying these transformations could be constructed using the telescoping languages framework.